Implantable adjustable drainage devices are known in the art, especially in the field of treatment of glaucoma.
Glaucoma is a disorder associated with high pressure in the eye, and is characterized by damage to the optic nerve, with consequent visual loss, initially peripheral, but potentially blinding if relentlessly progressive. Unfortunately, glaucoma is usually a disease in which the patient is entirely asymptomatic (without symptoms) until late in the disease. Glaucoma affects about 70 millions of people worldwide.
While traditional treatment of glaucoma is through medication for example eye drops lowering the production of intraocular fluid (aqueous humor), in certain cases this treatment fails and other surgical treatments are preferred, such as filter procedures or placement of a glaucoma drainage device (“GDD”) with a drainage tube. GDDs help evacuate intraocular fluid by providing an artificial drainage pathway, thus maintaining a low intraocular pressure (“IOP”).
Typically, the GDD is inserted through a small incision made in the conjunctiva. The surgeon then makes a tiny incision in the sclera of the eye and fashions an opening for the drainage implant device. The drainage tube is placed such that the opening of the tiny tube is inside the anterior chamber of the eye where it is bathed in aqueous fluid. The tube is sutured in place with the drainage device attached to the sclera of the eye. Most surgeons will place an absorbable suture around the tube at the time of surgery to prevent filtration through the device until a fibrous capsule has formed. As such, the device is not expected to function until about 3 to 8 weeks following the procedure. This technique is thought to prevent over-filtration.
A glaucoma passive drainage device of the prior art is described in U.S. Pat. No. 4,457,757 to Molteno. The Molteno device comprises in particular a tube made of a biologically inert silicone tubing for insertion into the eye in order to drain the aqueous humor from the anterior chamber of the eye. This device does not have a pressure regulating mechanism and only relies on the pressure regulation provided by the resistance to aqueous flow of the tubing.
One of the major problems of such device is that it is totally passive, i.e., the drainage flow depends on IOP and on the fixed hydrodynamic resistance of the shunt. In many cases, however, the hydrodynamic resistance of the shunt may not be optimal which may lead to high IOP, when the resistance is high, or to over-drainage, if the resistance is low.
This problem has been recognised in the prior art and several publications relate to improvements of the known device such that the flow can be controlled and adapted.
Another example is illustrated in U.S. Pat. No. 5,411,473 to Ahmed. In this patent, the idea is to add a system to a drainage device, in which the system has a membrane folded and held in tension between two plates to provide a slit opening. The membrane responds to pressure changes to open or close the slit opening. All the characteristics of the system are based on the properties of the membrane itself and this element cannot be changed easily.
Another example is illustrated in U.S. Pat. No. 5,300,020 to L'Esperance where the drainage system comprises flow control means. In this patent, said means are in the form of a plug of absorbable material having porous properties which maintains anterior chamber pressure. Once the aqueous fluid has been totally absorbed into the plug, a path of relatively slow drainage flow will be established into the subconjunctival space until an equilibrium of pressures is developed. The pressure release is slow enough to avoid a collapse of the cornea yet sufficient to lower the intraocular pressure.
As one will readily understand, a disadvantage of this solution is that it has certain inertia and the flow rate may not be changed to adapt to the circumstances.
In another embodiment disclosed in this patent, the system comprises a flexible drainage tube with a time-delay valve-opening structure. This structure comprises a ball of biocompatible absorbable material as means of applying a valve-closing squeeze on the tube. As the body fluid gradually dissolve the material of the ball, the valve-closing force of the ball is reduced to create a valve opening condition. In a further embodiment, the valve-opening structure comprises polymer components which either inherently or by reason of special compounding are selectively shrinkable or stretchable to effect opening and/or closure operation of the valve device.
In this embodiment, it is clear that a precise adjustment of the flow rate of the drainage is difficult to realize over time and once the ball has dissolved, it is not possible to regulate the flow anymore.
Other examples are disclosed in the following prior art publications U.S. Pat. No. 5,626,558, U.S. Pat. No. 6,186,974, U.S. Pat. No. 6,508,779 or U.S. Pat. No. 6,726,664.
U.S. Pat. No. 6,077,299 to Adelberg et al. discloses a non-invasively adjustable valve implant for the drainage of aqueous humor in glaucoma. An aim of the device disclosed in this patent is to provide an implant with a flow characteristic that can be adjusted in a non-invasive manner. More specifically, this device comprises an implant with an inlet tube that is surgically inserted in the anterior chamber of the eye allowing aqueous humor to flow from the anterior chamber to a valve. After passing through the pressure and/or flow regulating valve in the implant, the fluid is dispersed along the periphery of the implant to the interior of the Tenon's capsule where it is absorbed by the body. In one embodiment, the valve inhibits flow below and allows flow above a specific pressure difference between the intraocular pressure within the eye and the pressure within the bleb cavity in Tenon's capsule. The specified pressure difference or set-point is always positive and the valve is always closed for negative pressure differences to prevent reverse flow of fluid from the Tenon's capsule back into the anterior chamber of the eye.
In this patent, the valve is formed by a chamber to which the inlet tube is connected, said chamber being closed by pressure sensitive valve made of a flexible material, such as silicone, in the shape of a flat cone. The pressure regulation set point of the valve is governed by a flexible diaphragm cooperating with an armature plate having an inclined surface configured to slide over a complementary inclined surface that is attached to the diaphragm. The cooperation of the inclined surface of the plate and the complementary surface causes the diaphragm to deflect depending on where the armature plate is located. The armature plate itself is rotated to carry out this regulation through a rotor and a set of speed-reducing and torque-enhancing gears.
As one will readily understand, the characteristics of the valve depend strongly on one element that is the cone shaped valve. In addition, the regulating mechanism comprises many rotating parts and gears rendering it rather complicated to fabricate. In addition, because of the high number of moving parts, there is also a risk of malfunction of the device.
U.S. Pat. No. 6,168,575 and U.S. Pat. No. 6,589,198 to Soltanpour et al. disclose micro-pump assemblies that can be implanted in the eye for controllably removing excess fluid from the eye in order to treat glaucoma. In these patents, the implanted pumps have a variable pumping rate that can be adjusted either manually or automatically, controlled by the measured intra-ocular pressure. The disadvantage of such device is in particular the fact that they are complicated and expensive. Indeed, the device must contain all the necessary elements, in particular electronics and power source and since the device is implanted, these elements must be small and contained in a sealed enclosure. The risk of malfunction is also increased because of the high number of different elements present that must cooperate together.